Radiographic cameras utilized in providing an image of a radioactive subject are frequently composed of a scintillator crystal and a collimator for guiding radiant energy from the subject to the scintillator crystal. An array of photodetectors, such as photomultiplier tubes, face the scintillator for detecting scintillations. The collimators may be in the form of a parallel tube collimator, converging on diverging tube collimators or a pinhole aperture. In response to high energy radiations, such as gamma radiation or X-radiation emitted by the subject, the collimator produces an image of the subject upon the scintillator. Each high energy photon, such as a gamma photon, produces a scintillation in the form of a multiplicity of optical photons in the vicinity of the point of impact of the gamma photon within the scintillator. The points of impact of the gamma photons delineate the image of the subject. The optical photons are subject to internal reflection from the front face of the scintillator which faces the subject and, accordingly, the photodetectors which face the back face of the scintillator are responsive to both directly radiated and reflected optical photons. A transparent spacer, or light pipe, positioned between the scintillator and the photodetectors serves as an impedance match for the optical photons so that substantially all of the optical photons radiated through the back face of the scintillator impinge upon the photodetectors. The signals of the photodetectors are combined in a manner such as that taught in the U.S. Pat. No. 3,914,611 which issued to K. J. Stout on Oct. 21, 1975, the amplitudes of the signals of the photodetectors being weighted and summed to provide X and Y coordinate signals representing the positions of the points of incidence of the gamma photons upon the scintillator. The X and Y deflection signals are utilized to drive a display for showing an image of the subject.
A problem arises in that the image shown on the display should have the characteristics of both linearity and resolution, the linearity providing a minumum of distortion while the resolution insures that small, closely spaced, points of the subject can be distinguished in the displayed image. Heretofore, there has been a compromise in the design of radiographic cameras in that the photodetectors may be placed close to the scintillator to provide high resolution at the expense of linearity, or alternatively, the photodetectors may be placed further away from the scintillator to provide improved linearity with a loss of resolution.